Mobile computing devices, such as cell phones, smartphones, and tablet devices, increasingly utilize interactive displays that may be altered based on the position of a user relative to the mobile computing device. Knowing the distance between the user's head and the mobile computing device can be a powerful input mechanism. The mobile computing device can utilize the distance between the user's head and the mobile computing device to optimize the user experience. For example, when the user is far away, fonts can be made bigger to render the text more readable. The display also may automatically adapt to changes in the distance between the user's head and the mobile computing device based on gestures such as the user moving closer to the mobile computing device.
To provide this type of optimized viewing, the mobile computing device must be able to determine the distance between the user's head and the mobile computing device. The distance between the user's head and the mobile computing device can be determined based on the size of the user's head and their arm length. These values, however, are not generally known by the mobile computing device, would require additional user input, and would prevent optimal use of the mobile computing device by multiple individuals for whom the values may differ.